A worldwide interoperability for microwave access (WIMAX) system, also called an 802.16 wireless metropolitan area network (MAN), can cover data communication areas of 25 to 30 square miles.
The WIMAX technology is based on wideband radio standards among 802.16 series proposed by the Institute of Electrical and Electronics Engineers (IEEE). So far, the IEEE 802.16 series include seven standards: IEEE 802.16, IEEE 802.16a, IEEE 802.16c, IEEE 802.16d, IEEE 802.16e, IEEE 802.16f, and IEEE 802.16g. IEEE 802.16, IEEE 802.16a, and IEEE 802.16d are fixed radio access air interface standards, while IEEE 802.16e is a mobile wideband radio access air interface standard. WIMAX uses IEEE 802.16e as the air interface protocol.
IEEE 802.16e is compatible with earlier IEEE 802.16d. IEEE 802.16e and IEEE 802.16d are the same in physical layer implementation mode, and have the following difference: IEEE 802.16e has extended orthogonal frequency division multiple access (OFDMA) to meet different carrier bandwidth requirements. To support mobility, IEEE 802.16e introduces a number of new features in the media access control layer (MAC). By introducing new technologies such as orthogonal frequency division multiplex (OFDM) and multiple input multiple output (MIMO), the radio access technology develops towards higher capacity, wider coverage and mobility for a wideband radio system. The radio access technology coexists with and supplements the 3G network technology. Thus, the IEEE 802.16e technology has been a hot topic in the industry since its emergence.
Based on IEEE 802.16e, WIMAX proposes a new enhanced technology—IEEE 802.16m. Currently, IEEE 802.16m specifies the following requirements: Mobile objects at the speed of 350 kilometers per hour are supported; the maximum downlink data transmission rate should be over 350 Mbps; the uplink data transmission rate should not be smaller than 200 Mbps; the bandwidth ranges from 5 MHz, 10 MHz, 20 MHz to 40 MHz; and a maximum of 4×4 MIMOs can be used. When a 20 MHz bandwidth is used and communications are based on time division duplex (TDD), IEEE 802.16m requires that the downlink data transmission rate should be 40 Mbps and the uplink data transmission rate should be over 12 Mbps. In addition, IEEE 802.16m requires that the link layer access duration and handover delay should be less than 10 ms and 20 ms, respectively. Furthermore, IEEE 802.16m should be compatible with IEEE 802.16e.
The WIMAX system consists of base stations (BSs) and mobile stations (MSs). A BS communicates with an MS through electromagnetic waves transmitted and received by a radio transceiver. Each BS has a unique base station identity (BS ID), which is a 48-bit field. Each BS has its coverage, and may communicate with each BS in its coverage. Each BS sends a neighbor cell broadcast (MOB_NBR_ADV) message to BSs and MSs in a certain area on a timed basis, and stores the MOB_NBR_ADV message. The MSs receive and store the MOB_NBR_ADV message. The MOB_NBR_ADV message comprises BS IDs of the BSs in a certain area, where the BS IDs are arranged in sequence in the MOB_NBR_ADV message. Each BS may communicate with multiple MSs in its coverage at the same time. However, one MS can communicate with only one BS at the same time, and the BS is the serving BS of the MS. As the MS moves relative to the BS, the MS may go through coverage areas of multiple BSs. In this case, the serving BS of the MS may be changed. During the movement, the MS may use a different BS that meets communication quality requirements as its serving BS to continue its communications. This process is known as handover. To ensure the continuity of communications and reduces possible interruptions of communications due to the handover, the MS needs to detect the signal quality of each adjacent BS to determine a target BS for handover when maintaining normal communications with the current serving BS. This detection process is called scanning. In this way, the MS may be handed over to a new BS with better communication quality when handover is required. Thus, the scanning process is a key step to ensure smooth handover.
FIG. 1 shows a scanning process in the prior art. The scanning process message includes a mobile scanning response (MOB_SCN_RSP) and a mobile scanning request (MOB_SCN_REQ). A MOB_SCN-RSP message shall be transmitted by the BS either unsolicitedly or in response to a MOB_SCN-REQ message sent by an MS. By sending the MOB_SCN_RSP message, the BS notifies the MS receiving the MOB_SCN_RSP of the scanning start time, scanning type and BS ID of a BS to be scanned.
Both the MOB_SCN_RSP message and the MOB_SCN_REQ message include BS ID information. By carrying the BS ID information in the MOB_SCN_RSP message, the BS notifies the MS receiving the MOB_SCN_RSP message of which BSs are to be scanned. By carrying the BS ID information in the MOB_SCN_REQ message, the MS notifies its serving BS of which BSs are to be scanned. The MOB_SCN_RSP message and the MOB_SCN_REQ message also carry a scanning type field. Each BS ID in the MOB_SCN_RSP message and the MOB_SCN_REQ message corresponds to a scanning type.
In the prior art, the BS ID information in the MOB_SCN_RSP message and the MOB_SCN_REQ message is divided into two parts. The first part of BS ID information in the MOB_SCN_REQ message corresponds to the BS IDs included in an MOB_NBR_ADV message sent by the serving BS of an MS that sends the MOB_SCN_REQ message, and the second part is the IDs of BSs that are unsolicitedly scanned by the MS but not included in the MOB_NBR_ADV message. One part of the BS ID information in the MOB_SCN_RSP message corresponds to the BS IDs included in an MOB_NBR_ADV message of a BS that sends the MOB_SCN_RSP message, and the second part is full base station identities (Full BS IDs) sent by the BS, where each full BS ID is represented by 48 bits. Among the second part of BS IDs in the MOB_SCN_RSP message, some are sent by the BS to respond to the MOB_SCN_REQ message, and some are unsolicitedly scanned by the BS but not included in the MOB_SCN_REQ message.
Among the BS IDs in the scanning message, the part included in the MOB_NBR_ADV is represented in BS Index mode in IEEE 802.16e. That is, each of the BS IDs is represented by its sequence in the MOB_NBR_ADV message. The second part in the scanning message is represented in Full BS ID mode.
The number of BS IDs in the MOB_NBR_ADV message is usually smaller than 255. Thus, only 8 bits are needed in BS Index mode, while 48 bits are needed in Full BS ID mode. Compared with the Full BS ID mode, the BS Index mode saves 40 bits per BS requesting the scanning.
IEEE 802.16e uses the Full BS ID mode rather than the BS Index mode to represent the second part of the BS IDs because these BS IDs are not included in the MOB_NBR_ADV.
FIG. 2 shows a format of an MOB_SCN_REQ message in the prior art.
The MOB_SCN_REQ message is composed of fields, each of which is represented by a number or letter. The following describes each field.
Field 1 is a management message type field of 8 bits.
Field 2 is a scan duration field of 8 bits.
Field 3 is an interleaving interval field of 8 bits.
Field 4 is a scan iteration field of 8 bits.
Field 5 is an N_Recommended_BS_Index field of 8 bits. This field indicates the number of BS IDs that the MS intends to scan and that are included in the MOB_NBR-ADV message.
Field 6 is a “Configuration change count for MOB_NBR-ADV” field of 8 bits.
Field 7 is a Neighbor_BS_Index field of 8 bits. This field indicates the sequence of a BS ID that the MS intends to scan in the MOB_NBR_ADV message.
Field 8 is a reserved field of 1 bit.
Field 9 is a scanning type field of 3 bits. This field indicates the scanning type of the BS ID information mapped by field 7. The scanning type comprises scanning type 0, scanning type 1, scanning type 2, and scanning type 3.
Field 10 is an N_Recommended_BS_Full field of 8 bits. This field indicates the number of BSs that the MS intends to scan.
Field 11 is a Recommend BS ID field of 48 bits. This field indicates BS IDs of the BSs that the MS intends to scan.
Field 12 is a reserved field of 1 bit.
Field 13 is a scanning type field of 3 bits. This field indicates the scanning types of the BS IDs mapped by field 11.
When the value of field 5 is 0, fields 6-9 and field A are nonexistent.
Field A includes repeated contents of fields 7-9 in turn. The number of repetitions is equal to the value of field 5.
Field B includes repeated contents of fields 11-13 in turn. The number of repetitions is equal to the value of field 10.
Field C indicates one of other fields in the MOB_SCN_REQ message.
FIG. 3 shows a format of an MOB_SCN_RSP message in the prior art. The format of the MOB_SCN_RSP message is represented in the same way as that shown in FIG. 2. Fields 1-14 are 14 fields that are represented by numbers and arranged in ascending order, while fields 15-18 are four fields that are represented by numbers and arranged in ascending order. The following describes each field shown in FIG. 3.
Field 1 is a management message type field of 8 bits.
Field 2 is a scan duration field of 8 bits.
Field 3 is a report mode field of 2 bits.
Field 4 is a reserved field of 6 bits.
Field 5 is a report period field of 8 bits.
Field 6 is a report metric field of 8 bits.
Field 7 is a start frame field of 8 bits.
Field 8 is an interleaving interval field of 8 bits.
Field 9 is a scan iteration field of 8 bits.
Field 10 is an N_Recommended_BS_Index field of 8 bits. This field indicates the number of BS IDs that the BS intends to scan and that are included in the MOB_NBR-ADV message.
Fields 11-14 correspond to fields 6-9 shown in FIG. 2 in terms of content and meaning Field D between field 14 and field A is 24 bits long and is present only when the scanning type of field 14 is scanning type 2 or scanning type 3.
Field A shown in FIG. 3 includes repeated contents of fields 12-14 and field D in turn. The number of repetitions is equal to the value of field 11. Field D is located between field 14 and field A.
Field 15 is an N_Recommended_BS_Full field of 8 bits. This field indicates the number of BSs that the BS intends to scan and that are not included in the MOB_NBR_ADV message.
Field 16 is a Recommended BS ID field of 48 bits. This field indicates the BS IDs that the MS intends to scan and that are not included in the MOB_NBR_ADV message.
Field 17 is a reserved field of 1 bit.
Field 18 is a scanning type field of 3 bits. This field indicates the scanning types of the BS IDs in field 16.
Field D between field 18 and field B is 24 bits long and is present only when the scanning type of field 18 is scanning type 2 or scanning type 3.
Field B shown in FIG. 3 includes repeated contents of fields 16-18 and field D in turn. The number of repetitions is equal to the value of field 15. Field D is located between field 18 and field B.
Field E indicates one of other fields in the MOB_SCN_RSP message.